Plasma systems are of significance for production, processing and treatment of solid-state materials, among other applications. Plasma reactors, also known as plasma sources, can be used in many plasma processing applications, including, but not limited to, growth of thin films, dispersion, etching and cleaning. These plasma processing applications often require precisely-controlled application of excited or ionized particles. For example, the effects of ions, electrons and other energetic particles are now widely utilized for substrate cleaning as well as to assist and control film growth. Some of the particles do not just assist in the film growth but they may condense and thereby become part of the growing film or structure. These particles provide energy and momentum to the film growth process, resulting in densification, sputtering/etching, modification of stress, roughness, texture, etc.
Radio frequency (RF) plasmas are attractive as electron beam sources because they allow for a design where the cathode does not participate in electron production while providing high efficiency and long life operation. Traditionally, hollow cathodes or tungsten filaments have been used as electron sources because of their high electron current density and relatively low power requirements. However, their operational lifetime is limited by cathode and filament deterioration, contamination, and barium diffusion rates, and in some cases requiring a large amount of inert feed gas, thus rendering them less suitable for use in corrosive environments and sustained use.